PRINCIPLES OF CONTROL SYSTEMS Process ControlsSummaryBasic process control terms are summarized below.Process Control Term Definitions SummaryA control system is a system of integrated elements whose function is tomaintain a process variable at a desired value or within a desired range of values.Control system input is the stimulus applied to a control system from an externalsource to produce a specified response from the control system.Control system output is the actual response obtained from a control system.An open-loop control system is one in which the control action is independentof the output.A closed-loop control system is one in which control action is dependent on theoutput.Feedback is information in a closed-loop control system about the condition ofa process variable.A controlled variable is the process variable that is maintained at a specifiedvalue or within a specified range.A manipulated variable is the process variable that is acted on by the controlsystem to maintain the controlled variable at the specified value or within thespecified range.IC-07 Page 6 Rev. 0